Electrochemical production of solid oxides of carbon



Patented Aug. 23, 1 927.

UNITED. STATES PATENT, OFFICE. I

BRUCE K. BROWN, OF TERRE HAUTE, INDIANA, ASSIGNOR TO C. F. BURGESS LABORA- TORIES, INQ, OF DOVER, DELAWARE, A CORPORATION OF DELAWARE.

ELECTROCHEMICAL PRODUCTION OF SOLID OXIDES OF CARBON.

2N0 Drawing.

This invention relates to the electrochemical production of solid carbon oxide or oxides.

The solid oxide of carbon generally known 5 as graphitic oxide, or graphitic acid, was

first prepared by Brodie in 1859. (Phil. Trans, 149, p. 249, 1859). He used a mixture of potassium Chlorate and fuming nitric acid with which he treated Ceylon or similar graphite. He obtained a yellow or straw. colored solid end product which has since been shown to be a colloidal compound of carbon and oxygen. (Trans. Am. Electro. Soc., 1920, vol. '37,-p. 103). Because of its colloidal character water 1s always associated with it. It is not known whether'this is a mixture of oxides or a single definite oxide. This yellow oxide has the peculiar property of deflagrating when heated to a low temperature and may be recognized by this simple test.

I have discovered that this solid oxide of carbon will oxidize an acidified ferrous sulphatesolution such as is commonly used for the determination of the available oxygen in pyrolusite. (Jour. Ind. & Eng. Chem, vol. 9, p. 961, 1917). A large part of the oxygen is released fromthe solid oxide of carbon when treated with the ferrous sulphate and it is possible to determine the available oxygen content accurately in comparison to the cumbersome and inaccurate combustion methods previously used which only determined the total oxygen, and could not make adequate allowance for the water present.

While the Brodie method of preparing graphitic oxide is the one generally used by chemists, other chemical methods have been devised. All such methods are dependent upon strongly oxidizing mixtures usually containing one or more concentrated acids and an oxidizing salt. These mixtures oftenare explosive andare therefore dangerous to handle. In addition, the yields are low and the cost high, so that graphitic oxide has heretofore been but a laboratory curiosity. By my novel method I eliminate the use of strong acids and the danger of ex plosions. The yields are comparatively high so that the oxide of carbon may be made by my new method at a comparativelylow cost.

The only useknown to me to wh1ch graphitie oxide has been put in the past has Application filed July 7, 1925. Serial No. 42,091.

been in the testing of carbon compounds to determine the presence of graphite. Even this procedure has been the subject of much controversy. 'Someexperts maintain that graphite alone will produce graphitic oxide while others maintain that other forms of carbon will produce this yellow oxide. It is possible to produce a deflagrating oxide which oxidizes ferrous sulphate from forms of carbon other than the unctuous, highly crystalline products known as Ceylon or as Acheson graphite. Much uncertainty exists about the relation between the solid oxide or oxides of carbon and carbon in its various modifications.

)Vhile the yellow graphitic oxide is the end product generally desired, this end product requires the repetition of the oxidation a number of times. Since the oxidation proceeds from the exterior of the carbonaceous particle to the interior, the first oxidation is the most effective, as is shown by the oxygen determinations. The second and subsequent oxidizing liquids have to penetrate the colloidal enveloping oxide shell before they can oxidize the core of unchanged carbonaceous material. A particle of carbon, whether it is unctuous crystalline graphite or is highly calcined petroleum coke, after being given a first oxidation, may show little change in color from the original material. A highly crystalline graphite may show a greenish tinge while the highl calcined coke may not showany definite c ange. Under the microscope the surface shows a matte effect. Such a product, although almost black or dead black in color, may show as high as 10 percent of available oxygen due to the formation-of a solid oxide or oxides of carbon. It has the property of defiagrat-ing when heated and oxidizes acidified ferrous sulphate. It is, in effect, a shell of graphitic oxide or oxides with a core of unchanged carbon. No doubt it would be as effective as a particle of pure graphitic oxide for many purposes. As pointed out in my coqbending application Serial No. 42,090 filed July 7, 1925, such a Ipartiall oxidized particle of carbon may ave a vantages over fully oxidized carbon when used as a depolarizer in a dry cell.

I have discovered that carbon may be oxidized to a solid oxide or oxides having the properties of graphitic oxide when sub jected to electrochemical oxidation in certain electrolytes. Carbon so oxidized does not have the yellow color of pure graphitic oxide but has the dull black appearance of partially oxidized carbon. The electrochemical product deflagrates on heating, oxidizes f-erous sulphate in acid solution and acts as a depolarizer in a galvanic cell, showing that it is identical or approximately .identical with the product obtained by anode surface is suitable.

anode decomposes rapidly.

-'in any electrolytic operation.

carbon.

chemical oxidation.

I have found that dilute nitric acid is one of the most efiiective reagents to use as an electrolyte either alone or in'combination with other chemicals. The process may be carried out by suspending a slab of bonaceous material in the electrolyte as anode, using a cathode of suitable material, and passing an electric current through'as A. current density below 10 amperes per square foot of The carbonaceous anode, whether graphitic or but partly graphitic, gradually decomposes, a black sludge depositing in the bottom of the container or vat. The decomposition proceeds gradually from the exterior to the interior in much the same manner that metallic anodes are consumed. Gassing may occur at the cathode due to the release of hydrogen. By having a comparatively small surface at the cathode, the reducing action of the hydrogen is minimized and the hydrogen may be released largely as a gas. If a nitric acid electrolyte is used, the nitric acid is gradually reduced to nitrous acid or the lower oxides of nitrogen and may eventually be reduced to ammonia. As the nitric acid content of the electrolyte decreases below a certain concentration the yield of fixed oxygen decreases.

The black sludge is washed free of electrolyte. and preferably dried at a temperature below 100 C. so as to reduce the decomposition of oxide of carbon to a minimum.

, The electrolyte should be maintained at about room temperature 22 C.25 0., to secure the best results. If the temperature of the electrolyte rises to above 70 C. the yield-drops to practically nothing. .A high current density also decreases the yield. I have not determined whether the low yield is due tolocal heating which may accompany a high current density;

If the nitric acid content is too high, the

swells into a soft mass which is composed of various sized. particles of partially oxidized However, while the amount of sludge is'large, and the decomposition rapid, the amount of oxygen which is fixed is low. This makes the use of a strong nitric acid electrolyte undesirable. On examining such a decomposed anode it will be found to contain many large pieces of carbon rather than car- 7 It gradually the more uniform content of small particles obtained when aweaker acid is used. An electrolyte containing 30 per cent of nitric acid gives excellent results. \Vith an acid of this concentration, electrolyzed at a suitable temperature and with a suitable current density at the anode, the sludge will consist of a mixture of oxide of carbon and carbon and will contain at least 1 per cent by weight of available oxygen. Under favorable conditions it will contain 5 to 6 per cent of available oxygen as determined by the ferrous sulphate test. WVhile an electrolyte containing a much lower percentage of nitric acid may be used, the yields are not as satisfactory and the nitric acid is reduced much more quicklythan when an equal volume of stronger acid is used. In general, the best nitric acid concentration lies between 10 and 50 per cent by weight.

Although nitric acid alone may be used as an electrolyte, it is possible to improve the action of nitric acid so as to give alarger yield and higher percent of fixed oxygen. This improvement may be obtained by adding certain salts to the nitric acid, especially salts of an oxidizing nature, such as the chlorates and dichromates. Sodium dichromate, over a wide range of concentrations,

is especially effective in securing a high percentage of fixed oxygen in the product and a high yield for the current input. Five percent of sodium dichromate by weight, when added to a 30 per cent nitric acid electrolyte is a convenient and efiect-ive concentration. Sodium dichromate may be displaced by chromium trioxide with equally good results. During the electrolysis, the dichromate or chromium trioxide seems to prevent the escape of nitric oxide fumes from the surface of the electrolyte. These are noticeable when nitric acid is used alone.

Instead of using nitric acid as an electrolyte, it is possible to use the equivalent mixture of sulphuric acid and a nitrate such as sodium nitrate. Other acids may be used in place of sulphuric acid, which has the advantage of low cost. Dilute sulphuric acid; (5 to 15 per cent H. ,SO by weight) may be used as an electrolyte but the yield and the percent of fixed oxygen is low. Mixtures of sulphuric acid and oxidizing salts may be used.

A solution of sodium chlorate over a wide range of concentrations, may be used as electrolyte with good results. A mixture of sodium nitrate and sodium chlorate gives equally good results. To those skilled in the art these examples will suggest a large number of combinations of acids and salts.

In carrying on the electrolysis, the disintegration of the anode should be such that a large proportion of finely powdered product is obtained, preferably of a size to pass through a 20 mesh sieve. In this form, it

"to the greater area of the particles in proportion to the volume.

Carbon, as used herein refers to both amorphous and crystalline forms, but does not include the diamond.

I, claim:

1. The process of producing oxide of car-.

, bon solid under normal conditions consisting essentially of submitting graphite anodes to an electric current in a bath havin an oxygen containing oxidizing anion.

3. The process of producing a mixture of carbon and oxide of carbon solid under normal conditions consisting essentially of submitting carbon anodes to an'electric current in a bath having an oxygen containing oxidizing anion.

4. The method of producing oxide of car- .bon solid under normal conditions consisting essentially of submitting carbon anodes to an electric current at aztemperature below 70 C. in a bath having an oxygen containing oxidizing anion.

5. The process of producin oxide of carbon solid under normal con itions consisting essentially of submitting carbon anodes to an electric current in a bath at approximately room temperature having an oxygen containing oxidizing anion.

6. The process of producing oxide of carbon solid under normal conditions consisting essentially of submitting carbon anodes to an electric current with a current density below lO amperes per square foot'of anode surface in a bath having an oxygen containing oxidizing anion. v

7. The method of producing oxide of carbon solid under normal conditions consisting essentially of submitting carbon anodes to an electric current in an oxygen containing oxidizing acid electrolyte.

8. The method of producing'oxide of carbon solid under normal conditions consisting essentially of submitting carbon anodes to an electric current in an electrolyte containing nitric acid.

9. The method of producing oxide of carbon solid under normal conditions consisting essentially of submitting carbon anodes I to an electric current in an electrolyte containing from 10 to of nitric acid.

10. The method of producing oxide of carbon solid under normal conditions consisting essentially of submitting carbon anodes to an electric current in an electrolyte containing about 30% nitric acid by weight.

11. The method of producing oxide of carbon solid under normal conditions consisting essentially of submitting carbon anodes to an electric current in an electrolyte containing nitric acid and an oxidizing salt.

12. The method of producing oxide of carbon solid under normal conditions consisting essentially of submitting carbon anodes to an electric current in an electrolyte containing nitric acid and sodium dichromate. Y

13. The method of producing a solid oxide of carbon which consists in inserting an anode formed essentially of carbon in an oxygen containing oxidizing electrolyte together with a suitable cathode and passing an electric current through the electrolyte from the anode to the cathode at such current density and temperature as to disintegrate the anode, substantially as described. 14. The method of producing a solid oxide of carbon which consists in inserting anv anode formed essentially of carbon in an oxygen containing oxidizing electrolyte to-' gether with a suitable cathode and passing an electric current throu h the electrolyte sisting essentially ofv submitting an anodeconsisting in part at least of graphite to an electric current in a bath havlng an oxygen containing oxidizing anion.

In testimony whereof I aflix in si nature.

\ BRUCE K. R WN. 

